The present invention relates to devices for holding optical fibers, and in particular to devices for holding optical fibers organized in arrays.
Many fields of technology have benefited from the ability to transmit signals via waveguides such as optical fibers. In particular, optical fibers have enabled the construction of various types of local and long-distance communications networks. The signals propagating through an optical network are typically launched and out-coupled from individual optical fibers through their end facets. For example, in optical network components such as optical fiber switches and optical fiber cross connects, signals are out-coupled from one fiber and in-coupled into another fiber.
In accordance with well-known principles of optics, light emitted from the end facet of a fiber diverges in a cone-shaped pattern determined by the numerical aperture N.A.=n sin xcex8max of the fiber. In this equation n is the refractive index into which the fiber emits the light and xcex8max is the half angle of the cone shaped emission pattern.
In most optical networks and/or components it is important to minimize loss when connecting an optical fiber to an optical system. To accomplish this, the diverging light beams emitted by the optical fibers in the array are typically collimated and/or refocused by lenses. To effectively couple the individual fibers of a fiber array with other optical components or systems, the individual fibers and all other optical elements along the emitting and/or received light paths need to be precisely positioned and aligned. Specifically, precise alignment means that 1) light is emitted from each optical fiber at a precisely known position within the array, 2) light is emitted from each optical fiber at substantially the same angle (i.e., the optical fibers are aligned substantially parallel to each other), 3) light is emitted from each optical fiber at substantially the same distance from the collimating and/or refocusing lenses, and 4) each optical fiber has substantially the same numerical aperture.
The prior art teaches aligning optical fibers in an array of V-grooves. Such arrays typically include a small number of optical fibers (e.g., up to about 64) arranged in parallel in a single plane. For example, U.S. Pat. No. 6,027,253 to Ota et al. discloses an optical fiber array including a V-groove substrate having V-grooves on which optical fibers are arranged and a fiber fix substrate for fixing the optical fibers arranged on the V-grooves. Furthermore, V-groove arrays have also been adapted to requirements that fiber arrays be hermetically sealed to prevent ambient air from entering into the package holding the fiber array. A sealed fiber array and method for its manufacture using V-grooves is taught in U.S. Pat. No. 6,215,944 to Ota et al. Additional improvements to V-groove chips for fiber arrays having a wick stop trench to prevent adhesive moving via capillary action along the length of the V-groove are discussed in U.S. Patent Application Publication 2002/0003933 to Sherrer et al.
Other approaches to providing hermetically sealed packages for fibers are also known. For example, U.S. Pat. No. 6,216,939 to Thackara teaches a method for making a hermetically sealed package comprising at least one optical fiber feedthrough. The package has at least one solder perform between a sealing surface of a lid and a sealing surface of a housing. Applying pressure and heat so as to press the fiber or fibers into the solder seals the assembly. More general teaching on how to achieve fiber optic-to-metal connection seals can be found in U.S. Pat. No. 5,658,364 to DeVore et al.
Fiber arrays disposed on substrates with V-grooves and lodged between substrates as taught by Thackara are mostly suitable for constructing single-plane arrays. As the number of fibers increases such arrays become unwieldy. Many applications like, for example, in telecommunications are expected to require optical fiber arrays including more than one hundred (and potentially more than one thousand) optical fibers. Unfortunately, single-plane arrays are impractical for such applications. Moreover, efficient coupling of light output by an optical fiber array into another optical system becomes more difficult when aligning very large quantities of optical fibers than when dealing with only a few optical fibers.
Alternative approaches have been proposed in the prior art where high precision optical fiber arrays are more specifically adapted for dealing with larger numbers of fibers and two dimensional fiber arrays. For example, U.S. Pat. No. 5,907,650 to Sherman et al. teaches a high precision optical fiber array connector and method. In a most notable embodiment, the fibers are arrayed and positioned via openings of two masks spaced by a sandwiched layer. The openings are fabricated by laser cutting. A plurality of optical fibers include fiber ends having substantially truncated conical side surfaces that extend through the openings. When the conical surfaces engage the mask opening walls, a bonding material is applied to the mask forward face and exposed tips. After curing of the bonding material, the forward face is grinded and polished such that the exposed tips are made planar with the bonding material. The invention requires conical shaping of the fiber ends. Etching techniques are described as primary conical shaping techniques. The centering of a single fiber within an opening is accomplished as a line contact between the conically shaped cladding and an opening edge, which may result in damage of the cladding and an eventual loss in alignment precision. Also, all fibers have to be held with a certain force inside the openings to assure contact between the conical cladding and the corresponding opening edge during curing of the bonding material. In cases with a high number of fibers it may be difficult to hold each individual fiber with the required force during the curing process. The conical shape of the fiber ends is required for finding the openings and for centering the fiber ends in the assembly position. Damages of the fiber ends may occur as an eventual result of failed assembly attempts. Therefore, there exists a need for a method and apparatus that provides precise alignment of optical fibers without special treatment and/or fabrication effort of the fiber ends. The present invention addresses this need.
U.S. Patent Application Publication 2001/0051028 to Gutierrez et al. aims at providing a high-density fiber terminator/connector. The terminator/connector and method of making it comprise using deep reactive ion etching to etch a plurality of holes in a silicon substrate and placing fibers in the holes. The holes can be cylindrical in shape or non-cylindrical. Micro-machined kinematical alignment mechanisms or locators may be provided to position the optical fibers at the centers of the holes. The alignment mechanism includes elastic flaps concentrically placed around the assembled fibers and are intended to snuggly hold the fibers in position. Since the flaps deflect angularly a snuggly contact is questionable. Also, the flexible nature of the alignment mechanism may render it sensitive to bending momentums induced by the fibers themselves. To keep such bending moments to a minimum, pre alignment of the fibers is provided by slim conical hole sections fabricated below the flaps. Unfortunately, such slim conical hole sections result in a relatively small entry diameter making an insertion of the fiber end difficult to accomplish. Therefore, there exists a need for a structure that provides for an independent dimensioning of an insertion cone. The present invention addresses this need.
Although the teachings of Sherman and et al. and Gutierrez et al. address a number of the challenges in the way of a high precision array of optical fibers, their solutions are not sufficiently precise and robust for large arrays of optical fibers. What is needed is an optical fiber array that can accommodate a large number of fibers, achieve hermetic sealing and preserve excellent alignment of the fibers including planarity, parallel alignment, relative position between the fibers as well as absolute position of fibers in the array. Furthermore, it would be highly advantageous if such array would permit tuning of the orientation of the array in the holder.
In view of the shortcomings of the prior art, it is an object of the present invention to provide an apparatus for holding optical fibers in an array that satisfies the requirements of high alignment precision between fibers themselves and with respect to external devices. Specifically, the device of the invention is to provide excellent planarity, parallel alignment, relative position and absolute position of the optical fibers of the array.
It is another object of the invention to ensure that the device be sufficiently robust such that the precisely aligned fibers preserve their alignment over time.
It is yet another object of the invention to provide for a hermetic seal between the fibers, and especially the fiber ends and the external environment.
It is another object of the invention to provide the fiber housing with hermetic sealing from the external environment of the apparatus while attached to the apparatus
Still another object of the invention is to provide a mechanism for tuning the orientation of the array in the device.
These and other objects and advantages will become apparent upon reading the following description.
The objects and advantages of the invention are achieved with the aid of an insert for holding at least one optical fiber, and typically a large array of optical fibers. The insert has a top plate, a bottom plate and a spacer plate in the middle. An array of feedthroughs is provided by the insert for easily receiving and precisely positioning optical fibers. Each feedthrough includes two narrow hole sections on both ends of a wide hole. The wide hole is formed into the spacer plate, the narrow hole sections are fabricated in the top plate and the bottom plate. Adjacent to each narrow hole section is an expanding hole section that operates as a funnel during insertion of a fiber in the feedthrough. A fiber end is easily inserted in a feedthrough since the expanding sections capture the fiber end and center it on the narrow hole sections while the fiber end is moved forward. Consequently, a large number of fibers may be easily inserted and tightly positioned within the insert without need to particularly shape the fiber ends. Also, there is no need to hold the fiber ends in a certain position along the feedthroughs"" axes during the bonding of the fibers in the insert. This additionally simplifies the assembly procedure.
Spacing the two narrow hole sections apart provides for two defined positions for each fiber end. The orientation of the fiber end at the level of the output face remains substantially unaffected by eventual bending of the fiber in the proximity of the insert that might occur prior to bonding the fibers. As an advantageous result, the tilting of the fiber in the two narrow hole sections is so small that may be neglected.
In a preferred embodiment, the insert is employed in an apparatus designed for holding an optical fiber or an array of optical fibers. The apparatus has a fiber housing for mounting the insert. In one embodiment, the fiber housing has a front portion and the insert is mounted on the front portion. The fiber housing provides hermetic sealing from the external environment of the apparatus while attached to the apparatus.
The external housing has a glass plate disposed in a plane-parallel orientation relative to the insert. Thus, when the fiber housing is placed inside the external housing the glass plate is located parallel and next to the output face. Furthermore, in order to ensure proper optical out-coupling from the optical fibers, an optical gel is interposed between the glass plate and the insert.
A lens plate is positioned on top of the glass plate. The lens plate has a number of lenses arrayed in correspondence to the feedthrough array. Precise positioning of the lens plate is provided by an adjustment device that holds the lens plate while optical tests are performed. Once the optimal position of the lens plate is set, the lens plate is soldered to the external housing.
The details of the invention are presented in the below description with reference to the attached drawing figures.